Mechanism to Provide Reliability Through Packet Drop Detection

ABSTRACT

A method and a data processing system for completing checkpoint processing of a distributed job with local tasks communicating with other remote tasks via a host fabric interface (HFI) and assigned HFI window. Each HFI window has a send count and a receive count, which tracks GSM messages that are sent from and received at the HFI window. When a checkpoint is initiated by a master task, each local task forwards the send count and the receive count to the master task. The master task sums the respective counts and then compares the totals to each other. When the send count total is equal to the receive count total, the tasks are permitted to continue processing. However, when the send count total is not equal to the receive count total, the master task notifies each task of the job to rollback to a previous checkpoint or kill the job execution.

GOVERNMENT RIGHTS

This invention was made with United States Government support underAgreement No. HR0011-07-9-0002 awarded by DARPA. The Government hascertain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to the following co-pending U.S.patent applications, filed on even date herewith and incorporated hereinby reference in their entirety:

Attorney Docket No.: AUS920070330US1, entitled “Method, System andProgram Product for Reserving a Global Address Space;

Attorney Docket No.: AUS920070331US1, entitled “Method, System andProgram Product for Allocating a Global Shared Memory;”

Attorney Docket No.: AUS920070332US1, entitled “Notification to Task ofCompletion of GSM Operations By Initiator Node;”

Attorney Docket No.: AUS920070333US1, entitled “Issuing Global SharedMemory Operations Via Direct Cache Injection to a Host FabricInterface;”

Attorney Docket No.: AUS920070334US1, entitled “Mechanisms to OrderGlobal Shared Memory Operations;”

Attorney Docket No.: AUS920070335US1, entitled “Host Fabric Interface(HFI) to Perform Global Shared Memory (GSM) Operations;”

Attorney Docket No.: AUS920070336US1, entitled “Mechanism to PreventIllegal Access to Task Address Space by Unauthorized Tasks;”

Attorney Docket No.: AUS920070337US1, entitled “Mechanism to PerformDebugging of Global Shared Memory (GSM) Operations;”

Attorney Docket No.: AUS920070339US1, entitled “Mechanism to ProvideSoftware Guaranteed Reliability for GSM Operations;”

Attorney Docket No.: AUS920071056US1, entitled “Notification By Task ofCompletion of GSM Operations at Target Node;”

Attorney Docket No.: AUS920071057US1, entitled “Generating and IssuingGlobal Shared Memory Operations Via a Send FIFO;” and

Attorney Docket No.: AUS920080112US1 entitled “Mechanism forGuaranteeing Delivery of Multi-Packet GSM Message.”

BACKGROUND

1. Technical Field

The present invention generally relates to data processing systems andin particular to distributed data processing systems. Still moreparticularly, the present invention relates to data processing systemsconfigured to support execution of global shared memory (GSM)operations.

2. Description of the Related Art

It is well-known in the computer arts that greater computer systemperformance can be achieved by harnessing the processing power ofmultiple individual processing units. Multi-processor (MP) computersystems can be designed with a number of different topologies, of whichvarious ones may be better suited for particular applications dependingupon the performance requirements and software environment of eachapplication. One common MP computer architecture is a symmetricmulti-processor (SMP) architecture in which multiple processing units,each supported by a multi-level cache hierarchy, share a common pool ofresources, such as a system memory and input/output (I/O) subsystem,which are often coupled to a shared system interconnect.

Although SMP computer systems permit the use of relatively simpleinter-processor communication and data sharing methodologies, SMPcomputer systems have limited scalability. For example, many SMParchitectures suffer to a certain extent from bandwidth limitations,especially at the system memory, as the system scale increases.

An alternative MP computer system topology known as non-uniform memoryaccess (NUMA) has also been employed to addresses limitations to thescalability and expandability of SMP computer systems. A conventionalNUMA computer system includes a switch or other global interconnect towhich multiple nodes, which can each be implemented as a small-scale SMPsystem, are connected. Processing units in the nodes enjoy relativelylow access latencies for data contained in the local system memory ofthe processing units' respective nodes, but suffer significantly higheraccess latencies for data contained in the system memories in remotenodes. Thus, access latencies to system memory are non-uniform. Becauseeach node has its own resources, NUMA systems have potentially higherscalability than SMP systems.

Regardless of whether an SMP, NUMA or other MP data processing systemarchitecture is employed, it is typical that each processing unitaccesses data residing in memory-mapped storage locations (whether inphysical system memory, cache memory or another system resource) byutilizing real addresses to identifying the storage locations ofinterest. An important characteristic of real addresses is that there isa unique real address for each memory-mapped physical storage location.

Because the one-to-one correspondence between memory-mapped physicalstorage locations and real addresses necessarily limits the number ofstorage locations that can be referenced by software, the processingunits of most commercial MP data processing systems employ memoryvirtualization to enlarge the number of addressable locations. In fact,the size of the virtual memory address space can be orders of magnitudegreater than the size of the real address space. Thus, in a conventionalsystems, processing units internally reference memory locations by thevirtual (or effective) addresses and then perform virtual-to-realaddress translations (often via one or more intermediate logical addressspaces) to access the physical memory locations identified by the realaddresses.

Given the availability of the above MP systems, one further developmentin data processing technology has been the introduction of parallelcomputing. With parallel computing, multiple processor nodes areinterconnected to each other via a system interconnect or fabric. Thesemultiple processor nodes are then utilized to execute specific tasks,which may be individual/independent tasks or parts of a large job thatis made up of multiple tasks. In these conventional MP systems withseparate nodes connected to each other, there is no convenient supportfor tasks associated with a single job to share parts of their addressspace across physical or logical partitions or nodes.

Shared application processing among different devices provides a veryrudimentary solution to parallel processing. However, with each of thesesystems, each node operates independently of each other and requiresaccess to the entire amount of resources (virtual address space mappedto the local physical memory) for processing any one job, making itdifficult to productively scale parallel computing to a large number ofnodes.

SUMMARY OF ILLUSTRATIVE EMBODIMENTS

Disclosed are a method and a data processing system for completingcheckpoint processing of a distributed job across multiple nodes withlocal tasks communicating with other remote tasks via a host fabricinterface (HFI) and assigned HFI window. The HFI window has a send countand a receive count, which tracks GSM messages that are sent from andreceived at the HFI window. When a checkpoint is initiated by a mastertask, each task of the job forwards the value of the send count and thereceive count to the master task. The master task sums the respectivecounts and then compares the totals to each other. When the send counttotal is equal to the receive count total, the tasks are permitted tocontinue processing. However, when the send count total is not equal tothe receive count total, the master task notifies each task of the jobto rollback to a previous checkpoint or kill the job execution.

The above as well as additional objectives, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates an example multi-node data processing system with ahost fabric interface (HFI) provided at each node to enable GSMprocessing across the nodes, according to one embodiment of theinvention;

FIG. 2 illustrates the allocation of tasks of a single job acrosspartitions and nodes within a multi-node GSM environment (such as dataprocessing system of FIG. 1), according to one embodiment of theinvention;

FIGS. 3A and 3B illustrates two example allocations of global addressspace (GAS) among multiple tasks of a job to enable GSM operations,according to alternate embodiments of the invention;

FIG. 4 is a block diagram illustrating components of an example send(initiating) node and target node utilized for processing of GSMoperations, according to one embodiment of the invention;

FIG. 5 illustrates a detailed view of an example HFI window and theassociation of window entries to specific memory locations within thereal (i.e., physical) memory, in accordance with one embodiment of theinvention;

FIG. 6 is a flow chart of the method of initiating/establishing a jobwithin the GSM environment, including allocating tasks to specific nodesand assigning windows within the HFI, in accordance with one embodimentof the invention;

FIG. 7 is a flow chart illustrating the method by which the HFIprocesses a command generated by a task executing on the local node, inaccordance with one embodiment of the invention;

FIG. 8 is a flow chart illustrating the method by which the HFIgenerates and transmits a GSM packet, in accordance with one embodimentof the invention;

FIG. 9 is a flow chart of the method by which incoming GSM packets areprocessed by the HFI and the HFI window of a target/receiving node,according to one embodiment of the invention;

FIGS. 10 and 11 provide flow charts, which illustrate the methods bywhich the HFIs of the nodes on which the local tasks and a manager taskof a job executes/implements a checkpoint to ensure reliability ofmessage/operation transfers within the GSM environment, in accordancewith embodiments of the invention; and

FIG. 12 is a block diagram representation of entries within an exampleGSM command and GSM packet, in accordance with one embodiment of theinvention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The illustrative embodiments provide a method and data processing systemfor generating and processing global shared memory (GSM) operations thatcomplete parallel job execution of multiple tasks on different physicalnodes with distributed physical memory that is accessible via a single,shared, global address space (GAS). Each physical node of the dataprocessing system has a host fabric interface (HFI), which includes oneor more HFI windows with each window assigned to at most onelocally-executing task of the parallel job, although multiple windowsmay be assigned to a single task. The HFI includes processing logic forcompleting a plurality of operations that enable parallel job executionvia the different tasks, each of which maps only a portion of theeffective addresses (EAs) of the shared GAS to the local (real orphysical) memory of that node. Each executing task within a node isassigned a window within the local TAI. The window ensures that issuedGSM operations (of the local task) are correctly tagged with the job IDas well as the correct target node and window identification at whichthe operation is supported (i.e., the EA is memory mapped). The windowalso enables received GSM operations with valid EAs in the task to whichthe window is assigned to be processed when received from another taskexecuting at another physical node, while preventing processing ofreceived operations that do not provide a valid EA to local memorymapping.

In the following detailed description of exemplary embodiments of theinvention, specific exemplary embodiments in which the invention may bepracticed are described in sufficient detail to enable those skilled inthe art to practice the invention, and it is to be understood that otherembodiments may be utilized and that logical, architectural,programmatic, mechanical, electrical and other changes may be madewithout departing from the spirit or scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims.

Within the descriptions of the figures, similar elements are providedsimilar names and reference numerals as those of the previous figure(s).Where a later figure utilizes the element in a different context or withdifferent functionality, the element is provided a different leadingnumeral representative of the figure number (e.g, 1xx for FIG. 1 and 2xxfor FIG. 2). The specific numerals assigned to the elements are providedsolely to aid in the description and not meant to imply any limitations(structural or functional) on the invention.

It is understood that the use of specific component, device and/orparameter names are for example only and not meant to imply anylimitations on the invention. The invention may thus be implemented withdifferent nomenclature/terminology utilized to describe thecomponents/devices/parameters herein, without limitation. Each termutilized herein is to be given its broadest interpretation given thecontext in which that terms is utilized. Specifically, the followingterms, which are utilized herein, are defined as follows:

(1) Effective, virtual, and real address spaces: a user-level programuses effective addresses (EAs), which are translated into operatingsystem (OS)-specific virtual addresses (VAs). The OS and the hardwarememory management units (MMUs) translate VAs into real addresses (RAs)at the time of use.

(2) Node: the set of computing resources that form the domain of acoherent operating system (OS) image.

(3) Cluster: a collection of two or more nodes.

(4) System: the collection of all nodes in the cluster domain.

(5) Parallel Job: an application that executes on some or all the nodesin a cluster. A job is made up of tasks (processes), each of whichexecutes in a node domain in the cluster. A parallel job has variousattributes including a job ID that uniquely identifies the paralleltasks that comprise the parallel job in the entire system.

(6) Task: a single process that executes within a single effectiveaddress (EA) space. By definition, a task executes wholly within a node.However, multiple tasks in a parallel job may execute on the same node(typically proportional to the number of CPUs on the node). A task caninclude one or more threads of control that all view and share the sameeffective address (EA) space.

(7) Global shared memory (GSM)-enabled job: a parallel job, in which thecomponent tasks have arranged to make parts of their individualeffective address (EA) spaces accessible to each other via global sharedmemory (GSM) operations.

(8) Global address space (GAS): the union of all effective addresses(EAs) in a GSM job that are accessible to more than one task via GSMoperations.

(9) Global address: an effective address within a task described as <T,EA> that is accessible to other tasks.

(10) Home: the specific node where a particular location in the globaladdress space (GAS) is physically allocated in physical memory. Everylocation in the GAS has exactly one home.

As further described below, implementation of the functional features ofthe invention is provided within computing nodes and involves use of acombination of hardware and several software-level constructs. Thepresented figures illustrate both hardware and software componentswithin an example GSM environment in which two physically separatenodes, interconnected via respective HFIs and an interconnect, provide adata processing system that executes a parallel job as individual tasksthat utilize a GSM. The presentation herein of only two nodes, i.e., aninitiating (sending) node and a target (receiving) node, is providedsolely to simplify the description of the functionalities associatedwith GSM operations and the HFI. It is appreciated that this GSMfunctionality enables scaling to a much larger number of processingnodes within a single data processing system.

With specific reference now to the figures, and in particular to FIG.1A, there is illustrated a high-level block diagram depicting a firstview of an exemplary data processing system 100 configured with twonodes connected via respective host fabric interfaces, according to oneillustrative embodiment of the invention, and within which many of thefunctional features of the invention may be implemented. As shown, dataprocessing system 100 includes multiple processing nodes 102A, 102B(collectively 102) for processing data and instructions. Processingnodes 102 are coupled via host fabric interface (HFI) 120 to aninterconnect fabric 110 that supports data communication betweenprocessing nodes 102 in accordance with one or more interconnect and/ornetwork protocols. Interconnect fabric 110 may be implemented, forexample, utilizing one or more buses, switches and/or networks. Any oneof multiple mechanisms may be utilized by the HFI 120 to communicateacross the interconnect 110. For example, and without limitation, HFI120 may communicate via a proprietary protocol or an industry standardprotocol such as Inifiniband, Ethernet, or IP (Internet Protocol).

As utilized herein, the term “processing node” (or simply node) isdefined as the set of computing resources that form the domain of acoherent operating system (OS) image. For clarity, it should beunderstood that, depending on configuration, a single physical systemmay include multiple nodes. The number of processing nodes 102 deployedin a given system is implementation-dependent and can vary widely, forexample, from a few nodes to many thousand nodes.

Each processing node 102 may be implemented, for example, as a singleintegrated circuit chip (e.g., system-on-a-chip (SOC)), a multi-chipmodule (MCM), or circuit board, which contains one or more processingunits 104 (e.g., processing units 104A, 104B) for processinginstructions and data. Further, each processing unit 104 mayconcurrently execute one or more hardware threads of execution.

As shown, each processing unit 104 is supported by cache memory 112,which contains one or more levels of in-line or lookaside cache. As isknown in the art, cache memories 112 provide processing units 104 withlow latency access to instructions and data received from source(s)within the same processing node 102 a and/or remote processing node(s)102 b. The processing units 104 within each processing node 102 arecoupled to a local interconnect 114, which may be implemented, forexample, with one or more buses and/or switches. Local interconnect 114is further coupled to HFI 120 to support data communication betweenprocessing nodes 102A, 102B.

As further illustrated in FIG. 1A, processing nodes 102 typicallyinclude at least one memory controller 106, which may be coupled tolocal interconnect 114 to provide an interface to a respective physicalsystem memory 108. In alternative embodiments of the invention, one ormore memory controllers 106 can be coupled to interconnect fabric 110 ordirectly to a processing unit 104 rather than a local interconnect 114.

In addition to memory controller, each processing unit 104 also includesa memory management unit (MMU) 105 to translate effective addresses toreal (or physical) addresses. These MMUs 105 perform EA-to-RAtranslations for tasks executing on processing nodes (e.g., node 102A)of data processing system 100. However, the invention also uses aseparate MMU 121, which is coupled to the local interconnect 114. MMU121 performs EA-to-RA translations for operations received from tasksoperating on remote processing nodes (e.g., node 102B) of dataprocessing system 100. In one implementation of processorconfigurations, MMU 121 may be integrated with HFI 120 so as to supportEA-to-RA address translations required by HFI and/or tasks utilizing HFIto complete GSM operations.

The HFI 120A and functional components thereof, which are describedbelow, enables the task(s) executing on processing units 104 a/104 b togenerate operations to access the physical memory 108B of other nodesthat are executing other tasks of the parallel job using EAs from ashared global address space (GAS) and a GSM. Likewise, HFI 120B enablesaccess by the task(s) on initiating node 102A to access physical memory108B when certain criteria are met. These criteria are described belowwith reference to FIGS. 4 and 9

Those skilled in the art will appreciate that data processing system 100of FIGS. 1A and 1B can include many additional components, which are notillustrated herein, such as interconnect bridges, non-volatile storage,ports for connection to networks or attached devices, etc. Because suchadditional components are not necessary for an understanding of thepresent invention, they are not illustrated in FIGS. 1A or 1B ordiscussed further herein.

The above described physical representations of nodes of an example dataprocessing systems 100 with HFIs supports the distribution of tasksassociated with a parallel job across multiple nodes within a largersystem with a GSM. FIG. 2 illustrates a high level view of processingmultiple tasks of a parallel job within an exemplary softwareenvironment for data processing system 100, in accordance with oneembodiment. In the exemplary embodiment, data processing system 100includes at least two physical systems 200 a and 200 b (whichrespectively provide processing nodes 102 a and 102 b of FIG. 1) coupledby interconnect fabric 110. In the depicted embodiment, each physicalsystem 200 includes at least two concurrent nodes. That is, physicalsystem 200 a includes a first node corresponding to operating system 204a 1 and a second node corresponding to operating system 204 a 2.Similarly, physical system 200 a includes a first node corresponding tooperating system 204 b 1 and a second node corresponding to operatingsystem 204 b 2. The operating systems 204 concurrently executing withineach physical system 200 may be homogeneous or heterogeneous. Notably,for simplicity, only one node of each physical system is utilized in thedescriptions of the GSM and HFI functions herein, although the featuresof the invention are fully applicable to tasks executing on any one ofmultiple nodes on a single physical system accessing physical memory ofother nodes on other physical system(s).

Each physical system 200 may further include an instance of a hypervisor202 (also referred to as a Virtual Machine Monitor (VMM)). Hypervisor202 is a program that manages the full virtualization orpara-virtualization of the resources of physical system 200 and servesas an operating system supervisor. As such, hypervisor 202 governs thecreation and destruction of nodes and the allocation of the resources ofthe physical system 200 between nodes.

In accordance with the present invention, the execution of parallel jobsin data processing system 100 is facilitated by the implementation of anew shared memory paradigm referred to herein as global shared memory(GSM), which enables multiple nodes executing tasks of a parallel job toaccess a shared effective address space, referred to herein as a globaladdress space (GAS).

Thus, under the GSM model employed by the present invention, dataprocessing system 100 can execute multiple different types of tasks.First, data processing system 100 can execute conventional (individual)Tasks C, F, G, K, L, P, Q, T, V and W, which are independently executedunder operating systems 204. Second, data processing system 100 canexecute parallel jobs, such as Job 2, with tasks that are confined to asingle node. That is, Tasks D and E are executed within the nodecorresponding to operating system 204 a 1 of physical system 200 a andcan coherently share memory. Third, data processing system 100 canexecute parallel jobs, such as Job 1, that span multiple nodes and evenmultiple physical systems 200. For example, in the depicted operatingscenario, Tasks A and B of Job 1 execute on operating system 204 a 1,Tasks H and J of Job 1 execute on operating system 204 a 2, Tasks M andN of Job 1 execute on operating system 204 b 1, and Tasks R and S of Job1 execute on operating system 204 b 2. As is illustrated, tasks ofmultiple different jobs (e.g., Job 1 and Job 2) are permitted toconcurrently execute within a single node.

With standard task-to-task operation, tasks running on a same node,i.e., tasks homed on the same physical device, do not need to utilizethe HFI and resolve EA-to-RA mapping beyond the standard page table. TheHFI and/or MMU components are thus not utilized when exchangingoperations across tasks on the same physical node. Where tasks arerunning on different physical nodes, however, the use of the MMU and HFIis required to enable correct EA-to-RA translations for tasks homed atthe specific node when issuing and/or receiving GSM operations.

Additional applications can optionally be executed under operatingsystems 204 to facilitate the creation and execution of jobs. Forexample, FIG. 2 depicts a job management program 206, such asLoadLeveler, executing under operating system 204 a 1 and a runtimeenvironment 208, such as Parallel Operating Environment (POE), executingunder operating system 204 a 2. LoadLeveler (206) and Parallel OperatingEnvironment (208) are both commercially available products availablefrom International Business Machines (IBM) Corporation of Armonk, NewYork. LoadLeveler (206) and POE (208) can be utilized as a convenienceto the user, but are not required. However, the described embodimentprovides for the availability of a privileged program to both bootstrapnon-privileged executables on the cluster nodes and to enable thenon-privileged executables to request and use node resources.

In the following descriptions, headings or section labels are providedto separate functional descriptions of portions of the inventionprovided in specific sections. These headings are provided to enablebetter flow in the presentation of the illustrative embodiments, and arenot meant to imply any limitation on the invention or with respect toany of the general functions described within a particular section.Material presented in any one section may be applicable to a nextsection and vice versa.

A. Task Generation and Global Distribution

The method for generating and distributing the tasks of a job (e.g., Job1, illustrated in FIG. 2), are described in FIG. 6. The executable ofthe program is supplied to the job management program 206, withuser-supplied execution attributes in a job command file. Theseattributes include the number of nodes on which the job needs toexecute. The job management program 206 generates a job ID (that isunique system-wide) and selects a set of nodes in the system on which toexecute the parallel job. The job management program 206 then invokesthe runtime system 208 for parallel jobs (e.g., (POE)). The runtimesystem 208 in turn spawns the user executable on the set of nodes thatthe job management program 206 allocated for the parallel job, and theruntime system 208 sets up state that permits each task to determine thetask's unique rank ordering within the parallel job. For example, in ajob with N tasks, exactly one task will have the rank order i, where0<=i<N. The runtime system 208 also provides the mapping (in the form ofa table) between the tasks and the physical nodes on which the tasks areexecuting. Setup operations performed by the job management program 206also permit the tasks to access interconnect resources on each clusternode.

In order to complete the processing by the HFI and other functionalfeatures of the invention, a system-level establishment (or systemallocation) of the global shared memory is required. FIGS. 3A-3Billustrate two embodiments of assigning tasks to address spaces withinthe global address space during setup/establishment of the GSMenvironment. The complete description of this process is presentedwithin co-pending patent applications, Ser. Nos. ______ and/or ______(Atty. Doc. No. AUS920070330US1/AUS920070331US1). Relevant content ofthose applications are incorporated herein by reference.

During initialization of the tasks of a parallel job, each task issues asystem call to set up the global address space. In addition to reservingeffective address space, the system call also accomplishes twoadditional tasks. First, the call initializes a HFI window hardwarestructure in preparation for usage in the global shared memory model.Second, the system call creates a send FIFO and a receive FIFO, whichallow the task to send active messages to one another via the node'sHFI.

Once the global address space has been initialized, individual tasks canallocate physical memory that can be globally addressed by all tasks ofthe job. Memory allocation on each task is achieved through a secondsystem call, which specifies the amount of memory to be allocated, aswell as the effective address within the already-reserved global addressspace (GAS) where the allocated memory must appear. All allocations aredone locally with respect to the task issuing the second system call.Once allocation is completed, all threads within the locally-executedtask can access the allocated memory using load and store instructions.

In order to use the GSM feature, each of the group of tasks for the jobhas to communicate the results of the first system call and co-ordinateamongst each other the arguments to the second system call invocation.FIG. 6, described below, illustrates the method by which theseinter-task coordination of system calls are completed.

Referring now to FIG. 3A, there is depicted a representation of anexemplary effective address space of tasks of a parallel job followingthe establishment of the GAS. In the exemplary embodiment, parallel job300 comprising ten tasks, labeled Task 0 though Task 9. Each of the tentasks is allocated a respective one of effective address (EA) spaces302A-302 i by its operating system 204. These effective address spacesare allocated to each task independent of the existence of the othertasks. After each task issues an initialization system call, a portionof the effective address (EA) space on that task is reserved for useexclusively for performing global shared memory (GSM) allocations, asillustrated at reference numerals 304A-304 i.

With reference now to FIG. 3B, there is illustrated a representation ofan exemplary effective address space of tasks comprising a parallel jobfollowing the allocation of memory in the GAS 304A-304 i. In thedepicted example, the allocation for a shared array X[ ] distributedacross the GAS 304A-304 i is shown. In particular, region 306A isallocated to X[0]-X[9] in GAS 304A of Task 0, region 306B is allocatedto X[10]-X[19] in GAS 304B of Task 1, and so on until finallyX[90]-X[99] is allocated in region 306 i of GAS 304 i. The portions ofX[ ] allocated to the GAS 304 of a task are homed on the node executingthat task. Physical memory 308A-308 i is further allocated on eachtask's node to back the portion of X[ ] homed on that node.

FIGS. 3A and 3B provide two alternative methods though which the arrayx[] can be allocated. For instance, as shown in FIG. 3A, array x[] canbe allocated such that the array can be accessed with contiguouseffective addresses within the global address space of all ten (10)tasks participating in the parallel job. The global address space canalso be caused to begin at the same effective address on each task,through the co-ordination of arguments to the second system callinvocation. FIG. 6, described later, illustrates the method by whichthese inter-task coordination of system calls are completed. Sharedarray x[] can also be allocated in a non-contiguous manner within theglobal address space. Finally, the global address space can start atdifferent effective addresses within the tasks.

For the allocations in FIGS. 3A and 3B, the operating system of the nodeon which each task executes only allocates backing memory for thoseportions of the task global address space that are homed on that node.Elements 308 a through 308 i in each figure show how the physical memorymay be allocated to store the portion of the array x[] homed at thatnode. As shown, for tasks 0, 1, and 9, the allocation in FIG. 3A takesseven physical pages while that in FIG. 3B takes six physical pages.Every access to a shared variable in a GSM application must betranslated into a tuple of the form <T, EA>, where EA is the effectiveaddress on task T where the location is homed.

Practicality in data structure placement is a very importantconsideration since practicality can have a huge impact on the amount ofphysical memory required to support the allocation. For instance, if theprogrammer specifies that the shared array x should be distributed in acyclic manner, an extensive amount of fragmentation and wasted physicalmemory will result if the array were to be allocated such that the arraycan be contiguously addressed within the global address space. For suchan allocation, savings in the amount of physical memory required to backup the homed portions of x[] would be achieved by compacting the datastructure. The GSM feature described herein thus provides applicationswith considerable flexibility in deciding how to map global datastructures. As FIGS. 3A 3B show, simplicity in determining where ashared element is homed can be traded off against the fragmentationcosts of the chosen mapping scheme.

Using the above allocation of GAS to tasks of a job, the embodiments ofthe invention enables a job to be scaled across a large number of nodesand permits applications to globally share as large a portion of theapplication's effective address space as permitted by the operatingsystem on each node. Also, no restrictions are imposed on where thetasks of a job must execute, and tasks belonging to multiple jobs areallowed to execute concurrently on the same node.

B. HFI, HFI Window, Send and Receive FIFO, MMU and Memory Mapping

Referring now to FIG. 4, there is illustrated another more detailed viewof the data processing system 100 of FIGS. 1 and 2 with the hardware(and software) constructs required for generation, transmission, receiptand processing of GSM operations across physical nodes within the GSMenvironment. First computer node 102 a (initiating or sending node) andsecond computer node 102 b (target or receiving node) includes HFI 120a, 120 b, respectively. HFI 120 is a hardware construct that sits on thecoherent fabric within a (processor) chip. Each HFI 120 provides one ormore windows 445 (and 446) (see FIG. 5) allocated to a particularexecuting task of a parallel job.

When an executing task of a parallel job issues an initialization systemcall, the operating system (OS) of that node attempts to establish adedicated window on the HFI for that task. If the operation succeeds, aportion of the allocated HFI window is first mapped into the task'saddress space. The memory mapped IO (MMIO) space 460 includes a commandarea and FIFO pointers. After the appropriate portion of the task'seffective address space is reserved (i.e., mapped to the physicalmemory), the operating system sets up the window to point to the pagetable for that task so that effective addresses within inbound (i.e.,from the interconnect 410) GSM commands can be translated.

In processing system 100, first node 102 a represents thesending/initiating node and is illustrated with send FIFO 407 withinmemory 405 that is accessible via a MMIO 460. Second node 102 brepresents the receiving or target node and is illustrated with receiveFIFO 408 within its memory 406. It is understood that even though anasymmetric view is shown, both processing nodes 102 a and 102 b aresimilarly configured, having both send FIFO 407 and receive FIFO 408,and each node is capable of performing both send and receive functions.Within processing system, 100, the HFI 110 is the primary hardwareelement that manages access to the interconnect (410). The interconnectis generally represented by links 455 a, 455 b routing switch 410, and aseries of switch elements 450A, 450B and 460. HFI 120A thus enables atask executing on sending node (120 a) to send GSM operations (with adestination or target identified by the job ID, node ID and window ID)to a receiving/target node 102 b.

As further illustrated in FIG. 4, processing nodes 102 include at leastone memory controller 106, which is coupled to local fabric 414 toprovide an interface between HFI 120 and respective physical systemmemory (DIMMs) 408. Processing nodes 102 also include MMU 121, which iscoupled to fabric bus 414. MMU 121 may be a part of (i.e., integratedinto) HFI 120 and provides the EA-to-RA translation required for GSMoperation processing by the HFI 120. Coupled to fabric bus 414 isprocessor cache 412, which is in turn connected to processing units ofthe central processor. Also illustrated is (form the perspective of theexecuting task), a view of the mapping of EAs to physical memory space405 allocated to the executing task. Within this virtual view of thephysical memory is a send FIFO 407 which is used to store commands anddata generated by the task, prior to being processed by HFI 120 togenerate GSM operations. Also illustrated is HFI doorbell 409, which isa mechanism that tracks the number of operations within send FIFO, andis utilized to alert the HFI 120 when to retrieve operations from thesend FIFO 407. Similarly, receive FIFO 408 of target node 102 b islocated within physical memory 406, in which an EA mapping location 404is also identified for reference.

The HFI window 445 and 446 provide a task-level view into the node'shardware that enables GSM commands to be launched with regards to aparticular task's effective address space (302) and for the effectiveaddresses (EA) contained within commands to be appropriately translated.HFI windows 445 are basic system constructs used for GSM operations.Each HFI 120 may contain multiple windows 445, and each window isallocated to a single task of the one or more tasks executing on thecomputer node 102.

Further functional characteristics of example HFI windows 445 areillustrated by FIG. 5, which is now described. As shown by FIG. 5, HFI120 consists of a plurality of windows (window0 through windowN) ofwhich HFI window2 445 is selected as the example window. Each HFI has afixed number of windows, each of which can belong to exactly one task,although more than one window may be assigned to a task. The windowassigned to a task is used by the HFI 120 to both launch GSM messagesoriginating from the task as well as handle incoming messages accessingthat task's effective address space. HFI window 445 is accessible bytask-generated commands, which may be generated at different functionallevels, including by a user 550, an OS 552, and/or a hypervisor 554.

HFI window 445 consists of a plurality of functional entries, such ascommand entries, credentials entry, an address translation entry, anddata structures used by the HFI to control message transmission andreception. Specifically, as illustrated, window2 445 comprises thefollowing entries, without limitation, HFI command count 510, send FIFOEA 514, SEND RDMA FIFO EA 515, receive FIFO EA 516, epoch vector EA 518,credentials 512, and checkpoint counters 521/523. In the illustrativeembodiment, credentials 512 includes the job ID (also referred to hereinas a job key), process ID, LPAR (logical partition) ID and EA key. TheHFI references the credentials 512 to correctly authenticate an incomingGSM transaction as being authorized to perform an operation on theassociated task's effective address space. It is appreciated that thedifferent components of credentials 512 may also be represented with itsown entry within HFI window 445. The checkpoint counters includecheckpoint send counter 521 and checkpoint receive counter 523, whichare provided to count how many messages (i.e., GSM packets) were sentthrough the window and how many messages were received through thewindow of the particular task. The applicability of these checkpointcounters to GSM operations is described below within Section E andillustrated by FIGS. 10 and 11. Each of the above entries are registersproviding a value of a memory location at which the named entry isstored or at which the named entry begins (i.e., a start location)within the effective address space of the task. These effectiveaddresses are translated by MMU 121 into corresponding real addressesthat are homed within the physical memory 530. HFI forwards one of theeffective addresses of Window contents to MMU 121, and MMU 121translates the effective address into a real address corresponding tothe physical memory 530 to which the EAs of the task identified by thecredentials are mapped.

HFI window 445 also comprises one or more fence counters 520 fortracking completion of GSM operations during a local fence operation anda global fence operation. The fence counters 520 referenced by the EAsin map to fence counter 540 within the real memory location assigned tothe task. In order to assist with local (task-issued) fence operations,the RA space assigned to the task also includes a send-op counter 542 totrack the completion of task-issued commands, which are initially storedin send FIFO 532, before passing to HFI window for processing.

Thus, as further illustrated, send FIFO EA 514 holds the start effectiveaddress for the task's send FIFO, which address can be translated by MMU121 to point to the start (real address) of send FIFO 532 in physicalmemory 530. Likewise, receive FIFO EA 516 holds the start EA of thetask's receive FIFO 534, which address is translated by MMU 121, andpoints to the start address in physical memory 530 of the receive FIFO534 of the task. The SEND RDMA FIFO EA 515 and epoch vector EA 518similarly can be translated by MMU 121 to point to the start realaddresses of the SEND RDMA FIFO 536 and Epoch vector 538, respectively.Note that while the send FIFO 514 and receive FIFO 516 may be contiguousin the effective address space of the task to which that windowcorresponds, these FIFOs (514, 516) may be discontiguous in real(physical) memory 530.

Each HFI window contains key resources including the pointer to theaddress translation tables that are used to resolve the effectiveaddress (with respect to a particular task) into a real address. Thewindow number within the HFI that is allocated for the GSMinitialization operation is returned back to the user as an opaquehandle, which may contain an encoding (embedding) of the node and windownumber, along with the effective address where the global address spaceis reserved within that task's effective address space. The languagerun-time takes on the responsibility for communicating each task'swindow identity to all other tasks that wish to issue GSM commands tothat task. If a task has multiple threads of control, atomicity to theHFI window has to be ensured either through normal intra-task lockingprimitives, or by assigning each thread its own distinct HFI window.Finally, HFI performance counters for all traffic based on that windoware also mapped into the task's address space. This permits the task toeasily monitor statistics on the interconnect traffic.

HFI windows may be shared amongst one or more logical partitions. If asingle node is partitioned, the operating system running on a partitionmay only have access to a subset of the total number of supportedwindows. The OS may further reserve a subset of these windows for kernelsubsystems such as the IP device driver. The remaining windows may beavailable for use by the tasks executing within that partition.

When a window is allocated on the HFI, the operating system tags thewindow with the identity of the job to which the task belongs. Duringissuance of GSM operations, all outgoing packets are automaticallytagged by the HFI with the job id. Outgoing packets also specify aparticular window on the destination/target node's HFI 120B in whosecontext the GSM effective address must be translated. The HFI comparesthe job ID contained within the GSM packet against the job id containedwithin the window. If the job ID's do not match, the packet is silentlydiscarded. Statistics that count such packets can be used to gentlydissuade system users from either unintentionally or maliciouslyflooding the system with such packets.

Thus, unauthorized access to a task's effective address space is notpermitted during the course of global shared memory operations. A taskis able to send a GSM operation to any task belonging to any job runninganywhere in the entire system. However, the HFI will perform the GSMoperations on the targeted task's effective address space if and only ifan incoming GSM command belongs to the same job as the task whoseaddress space the command manipulates. A further granulation of job IDsis also possible, whereby a task can give specific authorization to onlya subset of the tasks executing within the job. This can be done by asubset of the tasks requesting a different job ID to be associated tothem, causing that job ID to be installed into the HFI window associatedwith these tasks.

In order to fully appreciate the functionality of each of the abovelisted entries and the entries use during GSM operation to retrievevalues from within physical memory 430, a description of the process ofassigning a window to support a task of a parallel job is now provided.This process is illustrated by FIG. 6, which is now described.Generally, FIG. 6 is a flow chart of the method of initiating a jobwithin the GSM environment and allocating the various tasks of the jobto specific nodes and assigning a window within the HFI of those nodesto a task, according to one embodiment of the invention.

The process begins at block 602, and proceeds to block 604, at which anapplication generates and issues a GSM initialization operation tolaunch a parallel job. Initialization of the job leads to allocation ofa plurality of tasks to certain nodes across the distributed network, asshown at block 606. At block 608, mapping of these nodes with allocatedtasks is generated and maintained at each node. At each local node withone of these tasks, before using global shared memory, the taskestablishes (or is assigned) a dedicated window on the HFI for thattask, as provided at block 610. A portion of the allocated HFI window(including a command area and FIFO pointers—FIG. 5) is first mapped intothe tasks effective address (EA) space as shown at block 611. Themapping of EA-to-RA for the task is provided to the MMU 121, for lateruse by the HFI during GSM processing. Additionally, the unique job keyor job ID is embedded into the HFI window assigned to the task.

At block 612, the HFI window assignments for the various tasks arelinked to a generated node mapping for the job, and then at block 614,the runtime library communicates task-window identity to other tasks inthe job. This enables each task to be aware of the location of the othertasks and permits subsequent software operations that allocate memory todetermine on which node a certain variable allocated in the globaladdress space should be homed. After the appropriate portion of thetask's effective address space is reserved, the operating system sets upthe HFI window pointer(s) (page table pointer 522) to point to the pagetable for that task so that effective addresses within inbound (i.e.,from the interconnect) GSM commands can be translated at the node, asindicated at block 616. Send and receive pointers (514, 516) are alsoestablished within the HFI window 445 that are translated to specificphysical memory locations by MMU 121.

At decision block 618, the OS determines if the task has multiplethreads. When a task has multiple threads of control, the OS ensuresatomicity to the HFI window through normal intra-task lockingprimitives, as shown by block 620. Alternatively, a task may request aseparate window for each of its threads. At block 622, the window numberwithin the HFI 110 that is allocated during the GSM initializationoperation is returned back to the user space (task) 550 as an opaquehandle, along with the effective address where the global address spaceis reserved within that task's effective address space. Finally, atblock 624, HFI performance counters for all traffic based on that windoware also mapped into the tasks effective address space. This setup ofperformance counters permits the task to easily monitor statistics onthe interconnect traffic. The process then ends at termination block626.

C. GSM Operations

After a global address space is established and memory allocated asgenerally described above (FIG. 6), each task is able to perform thefollowing basic operations: (1) Reads or “gets” to memory; (2) Writes or“puts” to memory; and (3) Restricted atomic operations such as thosebelonging to the set {ADD,AND,OR,XOR,COMPARE_AND_SWAP, FETCH_AND_OP}.Ultimately, all GSM operations are relayed by interconnect messages to(and from) the nodes where a memory location is homed. The basic GSMoperations listed above therefore need to be converted into interconnectmessages that are processed at the appropriate home node. Furthermore,any response messages also need to also be processed at the sending node(i.e., the node receiving a response from a target node for a previouslysent GSM operation). The HFI, and specifically the HFI window allocatedto the particular task, is utilized to provide the hardware support forthese and other GSM-related functions. GSM commands are transmitted by atask to the HFI by simply writing to the memory mapped address space.

The below described embodiments enables different tasks in a (parallel)job to perform operations efficiently on the global address space of theparallel job by using a HFI to issue GSM operations across the fabric ofthe GSM environment. Among the operations that are performed are reads,writes, certain types of atomic operations, and higher level operationsthat can be constructed using one or more of these basic operations.Within GSM task execution, all operations refer to effective addresseswithin the constituent tasks of the GSM job. GSM operations arenon-coherent, can be issued by an application from user-space code, andhave a simple API (application programming interface) that they can beused by the compiler, library, or end-user.

In one embodiment, GSM task execution does not provide/supportload-store access to a location within the global address space that ishomed on a remote node. That is, when a particular global address spacelocation is homed on example target node, a task executing on adifferent node is not able to access the location using a load or storeinstruction. Rather, with GSM task execution, a GSM operation (such as aread, write or atomic operation) must be employed in order to access thelocation. However, the executing task utilizes load and storeinstructions from the PowerPC® ISA (instruction set architecture) toaccess GSM locations that are homed on the node where the task isexecuting.

Turning now to FIGS. 7-9, which provide flow charts illustrating themethods by which the HFI and the HFI window are utilized to enable GSMoperations across different physical nodes of a processing system.Although the methods illustrated in FIGS. 7-9 may be described withreference to components shown in FIGS. 1-5, it should be understood thatthis is merely for convenience and alternative components and/orconfigurations thereof can be employed when implementing the variousmethods. Key portions of the methods may be completed by the taskexecuting within data processing system (DPS) 100 (FIG. 1, 4) andcontrolling access to a GSM location of/on a target node, and themethods are thus described from the perspective of either/both theexecuting task and/or the HFI and HFI window. For example, referring toFIG. 4, a GSM operation is initiated by a task on node A 102 a to alocation that is homed in the effective address space of a task on nodeC 102 b.

GSM commands issued by a task are in the form of operations on locationswithin another task's effective address space. Consequently, theeffective address embedded in a GSM command is meaningless withoutknowing the specific task with reference to which the effective addressmust be translated into a real address. The HFI evaluates received GSMcommands from a local send FIFO before generating the corresponding GSMmessage rackets). HFI and HFI window functionality provides the abilityto launch GSM commands (i.e., interconnect messages) through user-spacecommands.

In the following description, the terms GSM packets, GSM messages, GSMoperations, and GSM data are interchangeably utilized to refer to anycomponent that is transmitted from a first HFI window of an initiatingtask to a network fabric and/or is received from the network fabric at asecond HFI window of a target task. GSM command refers simply to anytask-issued command that is intended to be processed by the HFI andissued to the network fabric. The task also provides non-GSM or standardcommands that are executed on the local processing node.

FIG. 7 illustrates the method by which the HFI generates GSM packetsfrom task-issued commands placed in a send FIFO (first-in first-out)buffer, in accordance with one embodiment of the invention. The processof FIG. 7 begins at block 702, and proceeds to block 704 at which thetask determines a target node in the system to which an EA is homedwithin the GSM. Before a task is able to issue a GSM command, the taskneeds to have or obtain knowledge of the destination node and thedestination node window for directing/addressing the local command. Inone embodiment, the run-time library ascertains the physical node onwhich the task is executing by looking up the mapping table that isgenerated by the POE when the job is first launched. The runtime libraryprovides the task with window information for the selected target node,as shown at block 706. At block 708, the task generates a command withthe destination node and window information included in the command. Itshould be noted that the POE mapping is provide for convenience only.The present invention allows the task identifier to encode thenode/window combination.

Referring to FIG. 4, as part of the command structure, the task on nodeA 102 a creates the GSM command. The command structure includes theidentifier (ID) of the destination/target node and the window on thedestination node against which the message must be examined. Specifyingthe window on the destination node versus specifying the task (executingon the destination node) simplifies the hardware implementation. For putoperations that involve long memory transfers, the task also includesthe start effective address and range information as part of thecommand.

Returning to the flow chart, as provided at block 710, the task writesthe command describing the operation into the send FIFO. These commandsaccumulate in initiating task's cache (FIFO) as the commands arecreated. At block 712, the task's initiator triggers/requests the HFItransmit the stored commands by updating the command countlocation/register, which is physically resident on the HFI window. Aspreviously described, the command count location is memory mapped intothe tasks address space of physical memory. This action constitutes“ringing” the HFI doorbell.

Referring again to FIG. 4, as the task creates GSM commands, the taskkeeps updating the number of operations that need to be handled by theHFI. Commands are created in the send FIFO 407 (FIG. 4), which is backedby local physical memory 408, and can be resident in the cache 405. Thesend FIFO resides in physical memory but is mapped into the task'saddress space and is cacheable by the task. After assembling one or morecommands, the task writes the number of assembled commands to the HFIwindow door bell location 409. In one embodiment, the door bell location409 is physically resident on the HFI 120, but is memory-mapped into thetask's effective address space. The commands at the doorbell location409 are retrieved by the HFI and utilized by the HFI to generate a GSMpacket (containing GSM operations, data or messages) that the HFItransmits to a target task via the network fabric.

In order to transmit a GSM operation, the HFI needs certain bufferresources. As these buffer resources become available, the HFI retrievescommands from the send FIFO. Thus, at decision block 714, HFI logicdetermines if HFI resources are available to transmit the command usingthe task-assigned window. When HFI resources are not currentlyavailable, the task may continue to place new commands (if any) in thesend FIFO, as shown at block 716. However, if there are HFI resourcesavailable, the HFI creates packet headers from the command informationand generates the GSM packets, as shown at block 718. For long putoperations, the HFI also translates the start address and fetches (DMAs)data from the local node. The retrieved data is used to create a GSMmessage. HFI data structures in the window assigned to the task are alsoreferenced/updated. The HFI window tags the job ID of the task to theGSM message, as shown at block 720. The job ID is maintained in the sendwindow and is included as part of every GSM message issued by the HFIwindow. At block 722, the HFI routes the message (as GSM packets)through the interconnect switch. Then, the process of generating the GSMpackets using the HFI ends at termination block 724.

FIG. 8 is a flow chart illustrating the method by which the HFIprocesses a received command from a task executing on the local node,according to one embodiment. The process begins at block 802 andproceeds to block 804 at which the HFI reads/receives the command(s)from the send FIFO when the HFI has the buffering resources necessary totransmit packets on the interconnect. The HFI also receives a count ofthe number of operations that need to be transmitted, so that theprocessor (104, FIG. 1) is decoupled from having to wait while the HFImay be busy transmitting prior commands. Each command either fullydescribes a GSM operation, or contains start and range information forlong “put” (i.e., write data to target) operations. In order tofacilitate GSM operations that operate on small amounts of data, acommand can also contain immediate data, provided the combined commandand data fit within a cache line of, for example, 128 bytes. If a putcommand is larger than some fixed size, the request is put onto the RDMAcommand send FIFO 515. This allows small data movement requests to behandled with higher priority than large data movement requests andprevents large transfers from blocking small transfers.

The HFI identifies the window associated with the task generating thecommands placed in the task's send FIFO, as shown at block 806. The HFIlogic then determines, at block 808, if the command is a legal GSMcommand. A legal GSM command includes the required target node andwindow identifiers, and an operation that is supported via GSMprocessing (e.g., a get, put, or atomic operation), and any otherparameter(s) for generating a GSM packet. When the command is not alegal GSM command, the HFI window discards the command as not supportedby GSM, as provided at block 816, and the HFI window provides anappropriate response/notification to the executing task, at block 818.

However, when the command is legal, the HFI completes a series ofoperations to generate the GSM packets from the command, as indicated atblock 810. Among these operations performed by the HFI are one or moreof (a) creating a packet header from the command information, (b)potentially fetching (via DMAs) data from the local node, and (c)generating the packets. The HFI window then tags the packet with the jobID at block 812, and termination block 820. In a system where theindividual nodes execute operating systems that do not trust oneanother, the installed job ID (206) can also be encrypted or hashed tomake it tamperproof.

In order to appreciate the generation and issuing of a GSM message(i.e., a GSM operation transmitted via multiple GSM packets) withsequence number and count tuples, an example GSM command andcorresponding example GSM packet are illustrated by FIG. 12. The GSMcommand 1200 includes, without limitation, the following entries, shownwithout regard to actual order: an operation type, which defines whetherthe operation is an atomic operation or a GET or PUT operation, forexample; the source effective address, EA_(S), of the operation, whichis mapped to the memory of the initiating/local task; the targeteffective address, EA_(T), which is mapped to a real address in thelocal memory of the target task; the number of memory locations affectedby the GSM operation; immediate data or the EA of the locally storeddata; and flags indicating whether and/or what type of notification thereceipt/completion of the operation requires. As shown, other entriesmay also be included within the command, and these entries are utilizedto create corresponding entries within the GSM operation generated bythe HFI.

FIG. 12 also illustrates an example GSM packet (of multiple packets)generated by the HFI in response to receiving a GSM command (for amessage that cannot be transmitted by a single GSM packet). As shown, inaddition to the above entries, GSM packet 1220 includes the HFI command(e.g., a remote addition operation), header information, including,without limitation and in no particular order: Job ID, which is theidentification of the globally distributed job (or application), whichID is provided to each GSM packet originating from a tasks of the job;epoch entry, which is set to an actual epoch value for particular typesof operations, when a guaranteed-once notification is assigned as thereliability mode. (A default value indicates a type of operationrequiring a guaranteed-once delivery as the reliability mode; local andremote HFI window and node identifying task and window parameters toidentify to which HFI window (or corresponding task) and at which node aGSMn HFI packet should be directed; and an index for a <sequence, count>n-tuple entry for tracking multiple GSM packets of a single GSMmessage/operation; and a count total of the number of expected packets.

D. Target/Receiving/Destination Node HFI Processing

When the message reaches the destination, hardware support provided byPERCS retrieves the data and sends the response back as a message. Theresponse message is also handled by the HFI of the initiating node,causing the retrieved data to be written to the memory location of theinitiating task. On the receive side of a GSM operation, the job ID inthe packet is compared with the job ID in the target window. If the IDsmatch, the GSM command specified in the message is carried out.

For get operations, the effective address is translated on the targetHFI through the use of MMU 121. Data is fetched from the memory locationof the translated real address, and the data is embedded into a composedmessage and sent back to the initiating task (node). For put operations,the appended data is written to the physical address obtained bytranslating the specified effective address where the data is to bewritten at the target node. In one implementation, GSM atomic operationsare carried out by the memory controller on board the processor chip,such as a Power7™ chip. The processor's internal bus is designed tosupport special transaction types for the atomic operations that areinitiated by the HFI.

FIG. 9 illustrates the method by which the HFI processesreceived/incoming GSM messages (packets) from an initiating node,according to one embodiment. The incoming packets are processed by theHFI using the job ID and EA-to-RA matching table of the target node. Theprocess begins at block 902 and proceeds to block 904 at which the HFIreceives a GSM packet from the interconnect (through the local switchconnection). The HFI parses the GSM packet for the job ID, at block 906.At block 908, HFI examines the job ID included in the message andcompares the job ID with the job ID associated with the various windowssupported/assigned within the HFI. A determination is made at block 910whether the job ID matches one of the supported job IDs. If the job IDof the packet does not match any of the job IDs, the packet isdiscarded, as provided at block 912, and the process ends at terminationblock 920.

In one embodiment, the HFI may also evaluate the window and/or task IDto ensure that the packet has arrived at the correct destination node.As with the job ID, the message is discarded if the window IDinformation does not match that of the target window that is specifiedin the message. Also, in one embodiment, a threshold number of falserequests may be established for each HFI window. When the number ofreceived GSM operations that do not have the correct jobID meets ofsurpasses the pre-established threshold number, an error condition isregistered, which triggers issuance of an administrative notification.

Returning to decision block 910, if the job IDs match, the HFIdetermines, at decision block 911, if a translation exists for the EAwithin the page table pointed to by the page table pointer (522, FIG. 5)within the HFI window. The translation is provided by MMU 121, which isaccessed by the HFI to complete the check for whether the EA-to-RAtranslation is homed on the local node. When no valid translation existsfor the EA received in the message, the local task associated with thewindow is interrupted, as shown at block 913. Several alternatives arepossible. One alternative is to send an error response to the initiatingnode which could then send a non-GSM message to request a validtranslation to be installed. Another alternative is for the interruptedtask to install the required translation, in turn sending an error tothe initiating task if the requested mapping does not exist on thetarget task. When a translation does exist within the page table, theHFI (via the page table) translates the effective address in thereceived message into the corresponding real address, as shown at block914. The translation is performed by referencing the page table that ispointed to within the HFI window. When the address is successfullytranslated, the operation specified by the message is carriedout/performed, as shown at block 916.

The operation is first presented on the internal fabric bus in the chip.The memory controller performs the operation on the memory DIMMs. If thelocations being modified reside on any cache, the cache locations areupdated in place, with the contents being injected into the cache. Atblock 918, the HFI window (via the task) generates and transmits aresponse packet, if such a response is required. The HFI also writesnotifications to the receive FIFO (either writing the notification tomemory or injecting the notification into the cache), as shown at block819. These notifications are visible in the (target) task's effectiveaddress space. The (target) task can also access the locations that weremodified by directly accessing the appropriate location in the (target)task's address space.

The message flows are similar for GSM atomic operations and GSM getoperations. In an atomic operation, the memory controller can performthe atomic operation. Cache injection does not take place for atomicoperations. For a get operation, the HFI does not perform the DMAoperation and instead retrieves (DMAs) data requested by the operation.The retrieved data is assembled into a message that is then sent back tothe initiating node. The HFI on the requester performs the functionsrequired to store the retrieved data into the initiating task'seffective address space.

E. Mechanism to Provide Reliability Through Packet Drop Detection

Forward progress of the application/job requires that all theoperations, both at the local level and GSM level (on the networkfabric), are completed in a timely manner. Given the large numbers ofGSM packets placed by the multiple tasks on the network fabric, somemechanism is required to ensure that the GSM packets are being deliveredto their destinations and not simply being lost in the fabric. Accordingto the illustrative embodiments, two reliability modes are provided tomonitor reliability of GSM operations within the GSM environment. Thefirst reliability mode uses a combination of software and computersystem hardware support to detect, but not recover from lost packets. Inthe second reliability mode, detection of lost packets results in animmediate termination of the entire job. During implementation, the tworeliability modes are complementary, such that, the software guaranteedreliability mode will not affect the performance for the secondreliability mode where dropped packets cause application (job)termination.

E.1 Software Reliability Mode

As illustrated by FIG. 5, which is described above, during runtimeinitialization of the task and assignment and configuration of windowsfor the local tasks, every window is provided a pair of counters as apart of the internal data structures maintained by the HFI.Specifically, a message send counter 521 and message receive counter 523are provided to count how many messages (i.e., GSM packets) were sentthrough the window and how many messages were received through thewindow of the particular task. The HFI processing logic increments thecounters in the appropriate window every time a GSM message is sent orreceived, respectively. Since every window belongs to exactly one task,the send and receive message counters in a window can be attributed backto a specific task, and thus to a specific parallel job.

As each task finishes the task's execution (or at intervals throughoutthe task execution), the task determines the number of messages sent andreceived through the window allocated to the task. The language run-timelibrary provides a function, e.g., global_sent_received_count( ),utilized for this determination. This function is integrated into acheckpointing facility for GSM jobs. In one embodiment, the runtimedesignates one task of the multiple tasks associated with the job as themanager task and assigns the reliability functions of the overall job tothat manager task.

FIGS. 10 and 11 provide flow charts, which illustrate the methods bywhich the HFIs of the nodes on which the local tasks and a manager taskof a job executes/implements a checkpoint to ensure reliability ofmessage/operation transfers within the GSM environment, in accordancewith embodiments of the invention.

The process of FIG. 10 begins at block 1002 and proceeds to block 1004at which the runtime establishes the send and receive counters for thelocal task within the assigned window, and zeros the send and receivecounters, during task initialization. At block 1006, the applicationruntime selects/designates a manager task (from among the multipletasks) to perform the checkpoint calculation for the entire job, and atblock 1007, the runtime establishes the specific parameters for thecheckpoint (e.g., periodicity or checkpoint and wait time for receipt ofcheckpoint data from tasks).

Following these initialization steps, each HFI at the different nodesexecuting tasks of the parallel job monitors GSM operations in order toupdate the counters. At decision block 1008, the HFI logicdetects/checks whether a new GSM message (or GSM packet) is sent fromthe window of a local task to the fabric. If a new GSM message istransmitted by the HFI window, the HFI logic increments the send counter(maintained within the HFI window) for that task, as shown at block1010.

At decision block 1012, HFI logic checks when a GSM message is receivedat the HFI window from the fabric (from another task of the paralleljob). When a GSM message is received from remote tasks of the paralleljob, the receive counter is incremented, as shown at block 1014. Atdecision block 1016, HFI logic determines whether a checkpoint isreached for the job. The point at which a checkpoint is reached may bedetermined locally, based on checkpoint parameters, defining theperiodicity of the checkpoint or pre-set times for implementing thecheckpoint, for example. As another example, a checkpoint may be locallytriggered when the value of the send and/or receive counters of a taskexceeds a threshold value. When a checkpoint is reached, localcheckpoint processing is initiated, as shown at block 1018. As a part ofthe processing, each task requests the send and received counts from theHFI windows that the task has access to, and forwards the values of thecounts to the manager task. The tasks issue no further GSM messages, butincoming messages continue to be processed and the counters incremented.The HFI also waits for a notification/signal from the manager taskindicating whether to proceed processing beyond the checkpoint, redo themessage count check, or return to a previous checkpoint. When anotification is received, at block 1020, HFI determines at decisionblock 1022 if the notification is to proceed with processing beyond thecheckpoint. If the notification is to proceed with processing, a newcheckpoint is taken and the message counters are zeroed, as shown atblock 1024. The HFI also signals the task to continue processingoperations beyond the checkpoint, as provided at block 1026. In oneembodiment, the HFI does not interrupt the task execution during thecheckpoint and responds to the notification by simply not interruptingthe task. In this manner, the task may speculative execute beyond thecheckpoint, although no additional GSM operations of the task areaccepted for processing by the HFI until after the “continue processing”notification is received.

Returning to decision block 1022, if the notification is not to proceedwith processing, the HFI signals the task to roll back to a previouscheckpoint (for software guaranteed reliability mode operation) or tohalt execution (for the second reliability mode), as shown at block1028. The HFI then zeros the counters at block 1028 to enable trackingof later GSM messages when or if the task resumes execution.

Turning now to FIG. 11, which illustrates operations at the manager task(i.e., checkpoint processing performed via the HFI processing logic).The method begins at initiator block 1100 and proceeds to block 1102,which shows designated manager task receiving the signal/trigger toinitiate the checkpoint. At block 1104, the manager task issues acheckpoint request (for return of the send and receive counts for eachtask of the job) to the network fabric, which request includes the jobID associated with all tasks of the job. As described in related patentapplication Atty. Doc. No. AUS920070336 (Ser. No. ______), the HFIwindows assigned to the tasks of the job include the job ID and acceptsfor processing each received GSM message on the network fabric with thejob ID embedded therein. Thus, the tasks all receive and respond to thecheckpoint request. However, in one alternate implementation, the sendand receive counts are automatically transmitted from each task once thecheckpoint is reach. With this implementation, each task performs alocalized monitoring for the checkpoint.

Returning to the flow chart, the manager task initiates a waiting periodduring which the tasks are requested to respond to the request byforwarding the send and receive counters, as shown at block 1106. TheHFI also provides a delay period (which is a tune-able parameter in oneembodiment) to permit in-transit GSM packets to reach their destinationnodes and be counted. The manager task waits for this tune-able delay toprovide previously sent packets with an opportunity to get to theirdestination. This step is required because messages may still be intransit after the activation of the checkpoint. The delay period isprovided within the request and complied with by the tasks beforesending the send and receive counters. In one implementation, the delayperiod is a parameter that is established based on the length of timerequired for a GSM packet to traverse the network fabric from a firstnode to the furthest node on the fabric.

At block 1108, the manager task receives (and sums/accumulates) the sendand receive counts. Then, at decision block 1110, the manager taskdetermines whether all of the send and receive counts from each task hasbeen received. The manager task may maintain a count of the total numberof tasks executing within the job, and that number then represents thenumber of send counts and number of receive counts that should bereceived during checkpoint processing. When all of the send and receivecounts have not been received within the waiting period, the managertasks triggers a roll back to the previous checkpoint (if any), asprovided at block 1122, and issues a signal to the other tasks toperform the roll back to the previous checkpoint, at block 1124. Thetasks of the job then resume processing at the previous checkpoint, asindicated at block 1126.

When the full complement of send counts and receive counts have beenreceived by the master task, the master task, sums the send counts andsums the receive counts to yield a send count total and a receive counttotal, as provided at block 1112. The master task then compares the twototals and determines at block 1114 whether the send count total isequal to the receive count total. If the counts match, indicating GSMoperations sent by from one HFI window have all been received at thedestination HFI windows, the checkpoint for the overall job is updatedto the current point, as shown at block 1116. Also, the various countersand other parameters utilized during checkpoint processing are reset foruse in subsequent checkpoint processing. The manager task resumesexecution and transmits a global signal notifying all tasks toproceed/resume processing operations beyond the checkpoint, as shown atblock 1118. Processing of the tasks across the job resumes until thenext checkpoint is reached.

When the count totals do not match, however, the manage task initiates arollback to a previous checkpoint, as provided at blocks 1122-1126. Thecount totals are different when a GSM packet was dropped at some pointduring the job execution. In one embodiment, when the send count andreceive count totals do not match, the manager task generates a rollback message with a specific checkpoint indicated therein, rather than ageneral roll back message. Processing then resumes from the checkpointspecified within the roll back message. Also, in other embodiments, anerror notification is generated when a single count total does notmatch, or after a preset threshold number of checkpoint failures isencountered.

In each of the flow charts above, one or more of the methods may beembodied in a computer readable medium containing computer readable codesuch that a series of steps are performed when the computer readablecode is executed on a computing device. In some implementations, certainsteps of the methods are combined, performed simultaneously or in adifferent order, or perhaps omitted, without deviating from the spiritand scope of the invention. Thus, while the method steps are describedand illustrated in a particular sequence, use of a specific sequence ofsteps is not meant to imply any limitations on the invention. Changesmay be made with regards to the sequence of steps without departing fromthe spirit or scope of the present invention. Use of a particularsequence is therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

As will be further appreciated, the processes in embodiments of thepresent invention may be implemented using any combination of software,firmware or hardware. As a preparatory step to practicing the inventionin software, the programming code (whether software or firmware) willtypically be stored in one or more machine readable storage mediums suchas fixed (hard) drives, diskettes, optical disks, magnetic tape,semiconductor memories such as ROMs, PROMs, etc., thereby making anarticle of manufacture in accordance with the invention. The article ofmanufacture containing the programming code is used by either executingthe code directly from the storage device, by copying the code from thestorage device into another storage device such as a hard disk, RAM,etc., or by transmitting the code for remote execution usingtransmission type media such as digital and analog communication links.The methods of the invention may be practiced by combining one or moremachine-readable storage devices containing the code according to thepresent invention with appropriate processing hardware to execute thecode contained therein. An apparatus for practicing the invention couldbe one or more processing devices and storage systems containing orhaving network access to program(s) coded in accordance with theinvention.

Thus, it is important that while an illustrative embodiment of thepresent invention is described in the context of a fully functionalcomputer (server) system with installed (or executed) software, thoseskilled in the art will appreciate that the software aspects of anillustrative embodiment of the present invention are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the present invention applies equallyregardless of the particular type of media used to actually carry outthe distribution.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular system,device or component thereof to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed for carrying out this invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.Moreover, the use of the terms first, second, etc. do not denote anyorder or importance, but rather the terms first, second, etc. are usedto distinguish one element from another.

1. A data processing system comprising: a processing unit on whichexecutes a local task of a distributed job, wherein the distributed jobhas multiple tasks executing on nodes across a network fabric of aglobal shared memory (GSM) environment; a host fabric interface (HFI)having: a window allocated to the local task for sending and receivingGSM messages; processing logic for completing operations of the localtask and for completing checkpoint processing of the distributed job;wherein the other nodes are coupled to the data processing system viathe HFI; and wherein the processing logic further comprises logic for:receiving a plurality of send counts and receive counts from the othernodes executing tasks of the distributed job; summing the send counts ofeach other node and the local node together to generate a send counttotal; summing the receive counts of each other node and the local nodetogether to generate a receive count total; comparing the send counttotal with the receive count total; and when the send count total is notequal to the receive count total, issuing a notification to preventforward processing beyond the checkpoint by the local tasks and thetasks of the job at the other nodes.
 2. The data processing system ofclaim 1, wherein the processing logic further comprises logic forcompleting the functions of: determining when a condition occurs forinitiating the checkpoint processing; triggering a start of thecheckpoint processing at the other nodes by forwarding a checkpointrequest to the network fabric; activating a timeout period for receivingthe send counts and the received counts from the other nodes; andperforming said summing of the send counts and the receive counts at theend of the timeout period.
 3. The data processing system of claim 2,wherein said logic for activating a timeout period comprises logic forfactoring in a delay period within the timeout period to enable issuedGSM messages to arrive at the messages' destination nodes to update thereceive counts.
 4. The data processing system of claim 2, furthercomprising processing logic for: suspending local task processing andtask processing at the other nodes during the checkpoint processing; andwhen the send count total equals the receive count total, resuming localtask processing and task processing at the other nodes.
 5. The dataprocessing system of claim 1, wherein the condition that triggersactivation of the checkpoint comprises one or more of: passage of apreset period of time since one of (a) task initiation and a previouscheckpoint; (b) at least one of the send count, the receive count, andthe sum of the send and receive counts, at the local node passing apre-set threshold number of GSM operations at the local node; and (c) apreset global time associated with execution of the job.
 6. The dataprocessing system of claim 1, further comprising logic for: when acheckpoint request is received from one of the other nodes: determiningwhich local tasks belong to the job identified within the checkpointrequest; and forwarding the send counts and the receive counts of thelocal task belong to the identified job to the other node; wherein saidforwarding is performed after a delay period to enable GSM operations inflight to the local node to be received and counted in the receivecount.
 7. The data processing system of claim 1, wherein said processinglogic for issuing a notification further comprises logic for completingone or more of: directing the local task and tasks at the other nodes toroll back to a previous point of operation; resetting the send count andthe receive count of the local task; initiating a reset of the sendcount and the receive count of the tasks executing on the other nodes;and issuing at least one of a KILL operation for all tasks of the joband a restart operation of the job.
 8. The data processing system ofclaim 1, wherein when the send count total equals the receive counttotal, said processing logic further comprises logic for: triggering aresumption of processing when forward processing was suspended for thetask during the checkpoint operation; update a previous checkpoint tothe current point of operation and initiate monitoring for a nextoccurrence of the condition; zeroing the values of the send count andthe receive count at the local node; and generating and issuingnotification to the other tasks at the other node to resume taskprocessing and zero the send count and receive count of the other tasks.9. In a data processing system having: a processing unit on whichexecutes a local task of a distributed job, wherein the distributed jobhas multiple tasks executing on other nodes across a network fabric of aglobal shared memory (GSM) environment; a host fabric interface (HFI)having: a window allocated to the local task for sending and receivingGSM messages; and processing logic for completing operations of thelocal task and for completing checkpoint processing of the distributedjob; wherein the other nodes are coupled to the data processing systemvia the HFI, a method comprising: receiving a plurality of send countsand receive counts from the other nodes executing tasks of thedistributed job; summing the send counts of each other node and thelocal node together to generate a send count total; summing the receivecounts of each other node and the local node together to generate areceive count total; comparing the send count total with the receivecount total; and when the send count total is not equal to the receivecount total, issuing a notification to prevent forward processing beyondthe checkpoint by the local tasks and the tasks of the job at the othernodes.
 10. The method of claim 9, further comprising: determining when acondition occurs for initiating the checkpoint processing; triggering astart of the checkpoint processing at the other nodes by forwarding acheckpoint request to the network fabric; activating a timeout periodfor receiving the send counts and the received counts from the othernodes; and performing said summing of the send counts and the receivecounts at the end of the timeout period.
 11. The method of claim 10,wherein said activating a timeout period comprises factoring in a delayperiod within the timeout period to enable issued GSM messages to arriveat the messages' destination nodes to update the receive counts.
 12. Themethod of claim 10, further comprising: suspending local task processingand task processing at the other nodes during the checkpoint processing;and when the send count total equals the receive count total, resuminglocal task processing and task processing at the other nodes.
 13. Themethod of claim 9, wherein the condition that triggers activation of thecheckpoint comprises one or more of: passage of a preset period of timesince one of (a) task initiation and a previous checkpoint; (b) at leastone of the send count, the receive count, and the sum of the send andreceive counts, at the local node passing a pre-set threshold number ofGSM operations at the local node; and (c) a preset global timeassociated with execution of the job.
 14. The method of claim 9, furthercomprising: when a checkpoint request is received from one of the othernodes: determining which local tasks belong to the job identified withinthe checkpoint request; and forwarding the send counts and the receivecounts of the local task belong to the identified job to the other node;wherein said forwarding is performed after a delay period to enable GSMoperations in flight to the local node to be received and counted in thereceive count.
 15. The method of claim 9, wherein said issuing anotification further comprises: directing the local task and tasks atthe other nodes to roll back to a previous point of operation; resettingthe send count and the receive count of the local task; initiating areset of the send count and the receive count of the tasks executing onthe other nodes; and issuing at least one of a KILL operation to alltasks of the job and a restart operation for the job.
 16. The method ofclaim 1, wherein when the send count total equals the receive counttotal, said method further comprises: triggering a resumption ofprocessing when forward processing was suspended for the task during thecheckpoint operation; update a previous checkpoint to the current pointof operation and initiate monitoring for a next occurrence of thecondition; zeroing the values of the send count and the receive count atthe local node; and generating and issuing notification to the othertasks at the other node to resume task processing and zero the sendcount and receive count of the other tasks.
 17. A computer programproduct comprising: a computer storage medium; and program code on thestorage medium for completing checkpoint processing of a distributedjob, wherein the checkpoint processing is performed on a system having:a processing unit on which executes a local task of a distributed job,wherein the distributed job has multiple tasks executing on other nodesacross a network fabric of a global shared memory (GSM) environment; ahost fabric interface (HFI) having: a window allocated to the local taskfor sending and receiving GSM messages; and processing logic for;wherein the other nodes are coupled to the data processing system viathe HFI; and wherein said program code further comprising code for:receiving a plurality of send counts and receive counts from the othernodes executing tasks of the distributed job; summing the send counts ofeach other node and the local node together to generate a send counttotal; summing the receive counts of each other node and the local nodetogether to generate a receive count total; comparing the send counttotal with the receive count total; when the send count total is notequal to the receive count total, issuing a notification to preventforward processing beyond the checkpoint by the local tasks and thetasks of the job at the other nodes; and when the send count totalequals the receive count total, performing one or more of: triggering aresumption of processing when forward processing was suspended for thetask during the checkpoint operation; update a previous checkpoint tothe current point of operation and initiate monitoring for a nextoccurrence of the condition; zeroing the values of the send count andthe receive count at the local node; and generating and issuingnotification to the other tasks at the other node to resume taskprocessing and zero the send count and receive count of the other tasks.18. The computer program product of claim 17, said program code furthercomprising code for: determining when a condition occurs for initiatingthe checkpoint processing, wherein the condition that triggersactivation of the checkpoint comprises one or more of: passage of apreset period of time since one of (a) task initiation and a previouscheckpoint; (b) at least one of the send count, the receive count, andthe sum of the send and receive counts, at the local node passing apre-set threshold number of GSM operations at the local node; and (c) apreset global time associated with execution of the job; triggering astart of the checkpoint processing at the other nodes by forwarding acheckpoint request to the network fabric; activating a timeout periodfor receiving the send counts and the received counts from the othernodes, wherein said activating a timeout period comprises factoring in adelay period within the timeout period to enable issued GSM messages toarrive at the messages' destination nodes to update the receive counts;and performing said summing of the send counts and the receive counts atthe end of the timeout period.
 19. The computer program product of claim10, wherein: said program code further comprising code for: suspendinglocal task processing and task processing at the other nodes during thecheckpoint processing; and when the send count total equals the receivecount total, resuming local task processing and task processing at theother nodes; and said program code for issuing a notification furthercomprises: directing the local task and tasks at the other nodes to rollback to a previous point of operation; resetting the send count and thereceive count of the local task; initiating a reset of the send countand the receive count of the tasks executing on the other nodes; andissuing at least one of a KILL operation to all tasks of the job and arestart operation for the job;
 20. The computer program product of claim17, wherein when a checkpoint request is received from one of the othernodes, said program code further comprising code for: determining whichlocal tasks belong to the job identified within the checkpoint request;and forwarding the send counts and the receive counts of the local taskbelong to the identified job to the other node; wherein said forwardingis performed after a delay period to enable GSM operations in flight tothe local node to be received and counted in the receive count.